The present invention relates to a light emitting device used for a light source of a liquid crystal display and others. Particularly, the present invention relates to a light emitting device wherein clear and high-luminance emission without a color dapple can be acquired effectively utilizing the light emanating from a semiconductor luminous element for a long term.
A light emitting diode which is a semiconductor luminous element is a small device. Clear luminescent color can be efficiently acquired without anxiety that a light bulb is burnt-out. The light emitting diode has an excellent drive characteristic and is also strong against a vibration and repetitive switching operations. Therefore, the light emitting diode is utilized for a light source of various indicators and a liquid crystal display.
Heretofore, as a light emitting device of a liquid crystal display and others for displaying full color, a light emitting diode (LED) lamp is known. The LED lamp has semiconductor luminous elements emitting colors of red, blue and green, that is, three semiconductor luminous elements of so called RBG. The three semiconductor luminous elements are provided on a board as one unit.
Another type of full color light emitting device is also known. The full color light emitting device has three semiconductor luminous elements emitting colors of red, blue and green provided on a lead frame.
A light emitting diode used for this type of light emitting device has an excellent monochromatic peak wavelength. Therefore, in case that a light emitting device that emits white light is utilizing light emitting diodes that respectively emit red light, green light and blue light, for example, the light emitting diodes that respectively emit each color light are required to be arranged closely to diffuse and mix each color light.
Concretely, to acquire a light emitting device that emits white light, three types of red, green and blue light emitting diodes or two types of bluish green and yellow light emitting diodes are required. That is, to acquire a light emitting device that emits white light, light emitting diodes of plural types different in luminescent colors are required to be used.
In addition, a semiconductor light emitting diode chip has fluctuations in tone and luminance. In case that plural light emitting diodes are made of different materials, the driving power of each light emitting diode chip is different and a power source is required to be individually secured.
Therefore, to acquire the white light, a current supplied to every light emitting diode and others are required to be adjusted. There is a problem that a light emitting diode is different in temperature and aging characteristics, and tone also changes. Further, in case that the emission from each light emitting diode chip is not mixed uniformly, the light may include irregular color and desired white color may not be acquired.
Particularly, in the light emitting device wherein three types of semiconductor luminous elements of red, blue and green luminescent colors are provided on a board and are used as one unit, there is a problem that the light emitting device becomes large. In addition, as there is a distance between the semiconductor luminous elements, there is a problem that it is difficult to acquire uniform mixed color, and the color of the light emitting device becomes coarse.
In the light emitting device in which three types of semiconductor luminous elements of red, blue and green luminescent colors are provided on one lead frame and the like, to acquire the white luminescent color, charge is required to be supplied to all semiconductor luminous elements including red, blue and green. Therefore, there are a problem of large power consumption in view of energy conservation and a problem of a space required for a battery in a portable (mobile) type.
As a light emitting device in which the above-mentioned problems are solved, a light emitting device disclosed in Japanese published unexamined patent applications No. Hei 7-99345, No. Hei 10-190066 and No. Hei 10-242513 is known.
In the light emitting device disclosed in Japanese published unexamined patent application No. Hei 7-99345, an LED chip is mounted at the bottom of a cup. A resin (a color converting member) including a fluorescent material (or a filter material for partially absorbing the emission wavelength of the luminous chip) for converting the emission wavelength of the LED chip to another wavelength is filled inside the cup. Further, another resin is provided for surrounding the above-mentioned resin.
The light emitting device disclosed in Japanese published unexamined patent application No. Hei 10-190066 is provided with an LED chip fixed on a board by a die bonding member and a color converting member provided on the LED chip. The color converting member includes a fluorescent material that absorbs at least a part of light emitted from the LED chip, converts the wavelength and emits the converted light.
In a light emitting device disclosed in Japanese published unexamined patent application No. Hei 10-242513, a pair of mount-leads is provided in the light emitting device. A front edge of one of the mount-leads is in the form of a cup. An LED chip made of a gallium nitride semiconductor is arranged in the cup. The LED chip is electrically connected via an inner lead with the other mount-lead. A transparent resin including a fluorescent material is filled in the cup. In another light emitting device, a gallium nitride semiconductor chip is arranged in the body of the equipment and a transparent resin including a fluorescent material is filled in the body.
The light emitting device disclosed in the above-mentioned each patent application acquires another luminescent color from one type of luminescent color of a semiconductor luminous element itself. Concretely, as a light emitting diode that converts the wavelength of light emitted from an LED chip, white light emission is acquired by mixing light emitted from a blue light emitting diode and light emitted from a fluorescent material that absorbs the above-mentioned light and emits yellow light.
In the light emitting devices disclosed in the above-mentioned patent applications, the color converting member is provided on the LED chip. Therefore, in case that the white light is acquired, the dispersed blue light radiated upward from the LED chip itself and yellow light converted by the color converting member provided on the LED chip are mixed to look white light to a human eye.
To acquire clear and high-luminance white light, scattering and distribution of blue light and yellow light are required to be uniform and constant. However, in the configuration disclosed in the above-mentioned each patent application, the blue light is shielded by the color converting member on the LED chip. Luminance of the light emitting device is determined by a quantity of the light converted by the color converting member and the blue light radiated from the LED chip itself. Therefore, there is a problem that the scattering and the distribution of the color converting member are required to be uniform, and luminance is not satisfactory.
In addition to the color converting member including a fluorescent material for converting the wavelength of the light from the LED chip, a die bonding member (a mounting member) for fixing the luminous chip or the LED chip is required.
Further, the configuration disclosed in Japanese published unexamined patent application No. Hei 7-99345 has a problem that since the semiconductor luminous element is put in the wavelength converting material, it is difficult to acquire mixed color.
Also, in the configuration disclosed in Japanese published unexamined patent application No. Hei 10-242513, the gallium nitride semiconductor is arranged in the cup or the body of equipment. The fluorescent material such as a wavelength converting material is filled above the semiconductor and at the four sides. Hereby, the fluorescent material is uniformly dispersed in the transparent resin. In addition, there is a problem that it is difficult to control a dispersed quantity and a thickness at the four sides, and a dispersed quantity and a thickness above the surface. In addition to the configuration disclosed in the above-mentioned each patent application, there is also known another configuration. In the configuration, a blue light emitting semiconductor luminous element is enveloped in a shape of a lamp by the whole resin including a wavelength converting material. Hereby, white luminescent color can be acquired by the semiconductor luminous element lamp by converting the wavelength of light emitted from the semiconductor luminous element to another wavelength.
However, in the above-mentioned configuration, a quantity of the wavelength converting material is increased and the configuration has a problem in the stability of the scattering and the distribution of the wavelength converting material.
As described above, the light emission acquired in the case of the above-mentioned conventional type light emitting device is not enough as a light source for the liquid crystal display and others. Therefore, high-luminance light emission (particularly, white light emission) for a long term has been desired.
The invention is made to solve the above-mentioned problems. The invention has an object of effectively utilizing the light emanating from a semiconductor luminous element and acquiring clear and high-luminance light emission without a color dapple. The invention also has an object of providing light emitting device that enables acquiring high-luminance light emission for a long term compared with the conventional type.
A configuration of the invention to achieve the objects will be described below. A light emitting device according to the invention is provided on a reflecting surface of a base member (a board having reflectivity, a lead frame, and a pattern having reflectivity or an electric wiring pattern in a case), and includes a transparent resin in which a wavelength converting material is mixed and a transparent semiconductor luminous element provided on the transparent resin. In the light emitting device, a wavelength of light emitted from a lower surface of the semiconductor luminous element is converted by the wavelength converting material, and the light with the converted wavelength is reflected on the reflecting surface. The reflected light and light directly emitted from an upper surface of the semiconductor luminous element are mixed, and the mixed light is radiated from the upper surface of the semiconductor luminous element.
According to the light emitting device, light radiated downward from the lower surface of the semiconductor luminous element is reflected upward as the light with the wavelength converted by the wavelength converting material in the transparent resin. Hereby, the reflected light and light directly radiated from the semiconductor luminous element are completely mixed, and uniform light can be radiated upward from the upper surface of the semiconductor luminous element.
A conductive material may be further mixed in the transparent resin in addition to the wavelength converting material. When the semiconductor luminous element is bonded and fixed on the transparent resin, static electricity can be prevented from being electrified in the semiconductor luminous element itself.
The light emitting device according to a third aspect is characterized in that the transparent resin is formed in an area larger than an area of the semiconductor luminous element on the base member, and the semiconductor luminous element is bonded and fixed on the transparent resin on the base member.
According to the light emitting device, the light radiated downward from the lower surface of the semiconductor luminous element is reflected upward as the light with the wavelength converted by the wavelength converting material in the transparent resin. Further, light radiated downward from four sides of the semiconductor luminous element is reflected substantially upward as light with the wavelength converted by the wavelength converting material in the transparent resin provided in the area larger than the area of the semiconductor luminous element. The reflected light and light directly radiated from the semiconductor luminous element are completely mixed. Hereby, the uniform light can be radiated upward. The transparent resin is provided in the area larger than the area of the semiconductor luminous element. Hereby, when the wavelength converting material mixed in the transparent resin is applied or printed at a fixed and uniform thickness, mixed whole tone can be controlled not by the thickness but by the area. In addition, the transparent resin also functions as an adhesive and can fix the semiconductor luminous element.
A light emitting device according to a fourth aspect is characterized in that a concave portion is provided in the base member. The transparent resin is filled in the concave portion, and the semiconductor luminous element is bonded and fixed on the transparent resin filled in the concave portion.
According to the light emitting device, high-luminance light emission can be acquired, compared with a conventional type case that a transparent resin in which a fluorescent material is mixed is provided on a semiconductor luminous element. In addition, the semiconductor luminous element is bonded and fixed by the transparent resin filled in the concave portion. Therefore, the transparent resin also functions as an adhesive, so that it is possible to enhance and converge the light with the converted wavelength to be returned to the semiconductor luminous element.
A light emitting device according to a fifth aspect is characterized in that an aperture area of the concave portion is smaller than an area of the lower surface of the semiconductor luminous element.
According to the light emitting device, the direct light from the semiconductor luminous element and the light with the converted wavelength can be efficiently emitting outside.
A light emitting device according to a sixth aspect is characterized in that an inner wall of the concave portion faces the sides of the semiconductor luminous element and has an inclined face extending from the bottom to the aperture.
According to the light emitting device, the light radiated downward from the lower surface of the semiconductor luminous element is reflected upward as the light with the wavelength converted by the wavelength converting material in transparent resin. Further, the light is radiated from the four sides of the semiconductor luminous element sideway and downward. The radiated light is securely reflected substantially upward as the light with the wavelength converted by the wavelength converting material in the transparent resin formed on the inclined face at each position corresponding to the four sides of the semiconductor luminous element. The reflected light and light radiated directly from the semiconductor luminous element are completely mixed. Hereby, the uniform light can be radiated upward.
A light emitting device according to a seventh aspect is characterized in that an angle between the inclined face of the concave portion and the bottom of the concave portion is between 0xc2x0 and 45xc2x0.
According to the light emitting device, the light emanating sideway from the four sides of the semiconductor luminous element is reflected substantially upward. The light emanating slightly diagonally downward is reflected upward substantially toward inside of the semiconductor luminous element. The light emanating slightly diagonally upward is reflected upward toward outside of the semiconductor luminous element. Therefore, the light emanating from the four sides of the semiconductor luminous element can be effectively utilized.
A shape of the aperture of the concave portion in the light emitting device may be rectangular or circular depending upon a shape of the semiconductor luminous element. Hereby, the light from the lower surface of the semiconductor luminous element can be effectively projected onto the concave portion, and the machining is also easy.
In case that the concave portion is machined by etching, a laser beam or electric discharge, it is possible to precisely form the aperture in a small shape with good reflection efficiency. Therefore, the concave portion smaller than the size of the lower surface of the semiconductor luminous element can be provided.
The semiconductor luminous element may be also bonded and fixed on the transparent resin via a transparent adhesive. In this case, it is desirable that the semiconductor luminous element has an active layer arranged on a transparent substrate and a transparent electrode is provided on the active layer.
The base member used in the light emitting device may be a ceramic board, a liquid crystal polymer resin board and a glass fiber epoxy resin board, a lead frame and a case having reflectivity. Hereby, independent of a place and a material, the semiconductor luminous element is bonded and fixed anywhere and arbitrary mixed light such as white light can be acquired.
The semiconductor luminous element may be formed of InGaAlP, InGaAlN, InGaN or GaN. Hereby, the desired mixed light can be acquired depending upon a combination with the wavelength converting material mixed in the transparent resin.
In the light emitting device according to the invention, if the wavelength converting material mixed in the transparent resin is evenly distributed without being dispersed two-dimensionally, the light emanating from the semiconductor luminous element can be further effectively utilized, compared with the conventional type configuration in which the transparent resin with the fluorescent material is filled on the semiconductor luminous element at random.